A sputtering method of depositing a thin film on a substrate is a deposition method using an evacuated vacuum container. A target holder that holds a deposition source called a target made of a material to be deposited on a substrate and a substrate holder having a surface to place a substrate are installed in the vacuum container. An inert gas such as Ar or an inert gas such as nitrogen, or a process gas formed from a mixture of these gases is introduced into the vacuum container. A plasma is generated by applying a high voltage to the target, thereby adhering the target material to the substrate held by the substrate holder using the sputtering phenomenon of the target caused by charged particles in the discharged plasma.
When positive ions in the plasma enter the target material having a negative potential, the atoms or molecules of the target material are released from the target material. They are called sputtered particles. The sputtered particles adhere to the substrate and form a film containing the target material. In the sputtering apparatus, a shield plate capable of freely opening/closing, which is called a shutter, is normally provided between the target material and the substrate.
The shutter is mainly used for three purposes. The first purpose is to perform presputtering. In the normal sputtering apparatus, the plasma is generated not at the same time as the high voltage application but with a delay time of about 0.1 sec from the voltage application. Alternatively, no plasma may be generated even when the voltage is applied. Even if generated, the plasma may be unstable immediately after the start of discharge. Because of these phenomena, no film having a stable thickness and quality can be deposited. To avoid this problem, the shutter is used to execute so-called presputtering in which discharge is started while keeping the shutter closed, and the shutter is then opened after the discharge has stabilized so as to deposit the sputtered particles on the substrate.
The second purpose is to perform conditioning. Conditioning means discharge to be performed not to deposit sputtered particles on a substrate but to stabilize the characteristics of a deposited film.
For example, before the start of continuous deposition for production, discharge is performed under the same conditions as the continuous deposition conditions to stabilize the atmosphere in the vacuum container. Especially, in reactive sputtering for depositing an oxide or nitride of the target material by introducing a reactive gas such as nitrogen or oxygen or a gas mixture of a reactive gas and Ar, it is important for stable deposition to set the inner surface of the vacuum container to the same state as in continuous deposition. The reason for this is as follows. When a reactive gas is introduced into the vacuum container whose inner surface is covered with a film made of the target material, a bonding reaction occurs between the film and the reactive gas. For this reason, the atmosphere in the vacuum container does not stabilize, and no stable film characteristics can be obtained.
However, the sputtered particles adhere not only to the inner surface of the vacuum container but also to the substrate placing surface of the substrate holder. To prevent this, the shutter provided in the vicinity of the substrate holder is used. Discharge is performed by introducing an inert gas and a reactive gas into the vacuum container while preventing deposition on the substrate placing surface by closing the shutter to hide the substrate placing surface of the substrate holder viewed from the sputtering surface of the target but not to hide the inner surface of the vacuum container. A nitride or oxide thus adheres to the inner surface of the vacuum container. After the nitride or oxide is sufficiently adhered to the inner surface of the vacuum container in advance, deposition on the substrate starts. This allows the quality of the thin film deposited on the substrate to be stabilized.
In the conditioning, discharge may be performed under conditions different from the production conditions halfway through the continuous deposition for production. For example, when a high-stress film is continuously deposited on substrates by reactive sputtering, the film adhered to the inner surface of the vacuum container peels off due to the stress. The peeled film adheres to the substrate and degrades the characteristics of the electronic device. To prevent this, a low-stress metal film may periodically be deposited by nonreactive sputtering. For example, when a TiN film is continuously deposited, conditioning of Ti deposition is periodically performed. When only a TiN film is continuously deposited, the TiN film adhered to the anti-adhesion shield or the like in the vacuum container peels off. Periodically performing conditioning of Ti deposition allows to prevent this.
The third purpose is to perform target cleaning. Target cleaning is executed using the shutter when sputtering the contaminated or oxidized target surface in advance to remove the contaminated or oxidized portion of the target before continuous deposition before production. When manufacturing the target, the target is formed by machining using a lathe or the like in the final step. A contaminant generated from the grinding tool at this time adheres to the target surface. Alternatively, the target surface is oxidized during transportation of the target. It is necessary before deposition to sufficiently sputter the target surface to expose a clean target surface. In this case, sputtering is performed while keeping the shutter closed such that the contaminated or oxidized target particles do not adhere to the substrate placing surface of the substrate holder.
Against the backdrop of requirements for higher device performance, the target material that has adhered to the lower surface of a semiconductor substrate may diffuse into the semiconductor substrate upon annealing to degrade the device characteristics or may be brought in the subsequent step to contaminate the substrate processing apparatus from the next step. Contaminating another apparatus via the lower surface of the substrate has a large influence even if the target material adhesion amount to the lower surface of the substrate is very small, for example, about 1×1011 atms/cm2. For this reason, strict management is required.
The above-described problem arises because a gap is present around the shutter even when it is closed, and a very small amount of sputtered particles passes through the gap. That is, the sputtered particles adhere to the substrate placing surface of the substrate holder during conditioning or target cleaning. The sputtered particles adhere to the lower surface of the substrate to contaminate the substrate. In addition, the sputtered particles are transported to the next step to contaminate another manufacturing apparatus.
As a technique of avoiding the problem of sputtered particle wraparound at the time of target cleaning or presputtering, for example, PTL1 discloses a technique of installing a cylindrical cathode cover around a target and providing a shutter with a minimum gap with respect to an end of the opening of the cathode cover.
Each of PTL2 and PTL3 discloses an apparatus having two shutters between a substrate and a target or between a substrate and a deposition source.